Integrated circuit (IC) industry has experienced rapid growth. As the generations of ICs proceeds, the dimension is smaller while the structure is more complex. These advances have increased the standard of IC manufacturing, and development in IC processing and fabricating is needed. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has increased, while geometry size (i.e., the smallest component that can be created using a fabrication process) has decreased.
This scaling down process gives rise of a few issues, for example, current leakage and material compatibility. Particle penetration and unavoidable depletion effect occur in conventional polysilicon gate. Work function metals have been employed to replace the conventional polysilicon gate. Elevation in gate capacitance and reduction of gate dielectric layer are among the advantage of using metal gate stacks. However, undesired interaction between the metal gate stacks and the underlying dielectric material renders device performance poor.